1. Field of the Invention
The present invention relates to a heat spreader module which is used to cool, for example, an IC chip of a semiconductor or the like.
2. Description of the Related Art
In general, a heat spreader module, which is used as a member for effectively dissipating the heat generated by a semiconductor device such as IGBT (Insulated Gate Bipolar Transistor), is provided with a base for joining a heat spreader member to a heat sink which serves as a heat-releasing member, in addition to a joined unit of a circuit, an insulating substrate, and the heat spreader member (heat-diffusing layer).
Conventionally, the base is composed of copper. When the joined unit is joined to the base, the joining is performed by using a solder layer (melting point=about 250° C.) in many cases. In this procedure, the situation is to the extent that the base is exposed to the joining temperature for the solder layer for a short period of time. It has been unnecessary to consider the softening by annealing in such a degree that the strength is lost.
However, there have been factors to raise the production cost which causes a high price, because of the large heat resistance brought about by the solder layer and the route to pass through the two steps, i.e., the step of brazing and soldering the circuit and the insulating substrate and the step of joining the joined unit and the base.
In view of the above, the present inventors have previously disclosed, in Japanese Laid-Open Patent Publication No. 2002-43482, a technique in which any joining layer, which causes the heat resistance, is not allowed to remain by joining a circuit, an insulating substrate, and a base by using a hard solder material while applying a pressure, wherein the joining is performed in one step. According to this technique, it is possible to inexpensively obtain a heat spreader module which has a high coefficient of thermal conductivity.
However, in the technique in which the joining is completed in one step as described above, the base is heated up to the melting point of the hard solder material. Therefore, it is feared that the base may be softened. Further, it is feared that the base may be deformed with ease during the handing in the production process.